57 research outputs found
BrainFrame: A node-level heterogeneous accelerator platform for neuron simulations
Objective: The advent of High-Performance Computing (HPC) in recent years has
led to its increasing use in brain study through computational models. The
scale and complexity of such models are constantly increasing, leading to
challenging computational requirements. Even though modern HPC platforms can
often deal with such challenges, the vast diversity of the modeling field does
not permit for a single acceleration (or homogeneous) platform to effectively
address the complete array of modeling requirements. Approach: In this paper we
propose and build BrainFrame, a heterogeneous acceleration platform,
incorporating three distinct acceleration technologies, a Dataflow Engine, a
Xeon Phi and a GP-GPU. The PyNN framework is also integrated into the platform.
As a challenging proof of concept, we analyze the performance of BrainFrame on
different instances of a state-of-the-art neuron model, modeling the Inferior-
Olivary Nucleus using a biophysically-meaningful, extended Hodgkin-Huxley
representation. The model instances take into account not only the neuronal-
network dimensions but also different network-connectivity circumstances that
can drastically change application workload characteristics. Main results: The
synthetic approach of three HPC technologies demonstrated that BrainFrame is
better able to cope with the modeling diversity encountered. Our performance
analysis shows clearly that the model directly affect performance and all three
technologies are required to cope with all the model use cases.Comment: 16 pages, 18 figures, 5 table
A system architecture, processor, and communication protocol for secure implants
Secure and energy-efficient communication between Implantable Medical Devices (IMDs) and authorized external users is attracting increasing attention these days. However, there currently exists no systematic approach to the problem, while solutions from neighboring fields, such as wireless sensor networks, are not directly transferable due to the peculiarities of the IMD domain. This work describes an original, efficient solution for secure IMD communication. A new implant system architecture is proposed, where security and main-implant functionality are made completely decoupled by running the tasks onto two separate cores. Wireless communication goes through a custom security ASIP, called SISC (Smart-Implant Security Core), which runs an energy-efficient security protocol. The security core is powered by RF-harvested energy until it performs external-reader authentication, providing an elegant defense mechanism agai
Peak misdetection in heart-beat-based security: Characterization and tolerance
Abstract — The Inter-Pulse-Interval (IPI) of heart beats has previously been suggested for security in mobile health (mHealth) applications. In IPI-based security, secure communi-cation is facilitated through a security key derived from the time difference between heart beats. However, there currently exists no work which considers the effect on security of imperfect heart-beat (peak) detection. This is a crucial aspect of IPI-based security and likely to happen in a real system. In this paper, we evaluate the effects of peak misdetection on the security performance of IPI-based security. It is shown that even with a high peak detection rate between 99.9 % and 99.0%, a significant drop in security performance may be observed (between-70 % and-303%) compared to having perfect peak detection. We show that authenticating using smaller keys yields both stronger keys as well as potentially faster authentication in case of imperfect heart beat detection. Finally, we present an algorithm which tolerates the effect of a single misdetected peak and increases the security performance by up to 155%. I
Dirichlet sigma models and mean curvature flow
The mean curvature flow describes the parabolic deformation of embedded
branes in Riemannian geometry driven by their extrinsic mean curvature vector,
which is typically associated to surface tension forces. It is the gradient
flow of the area functional, and, as such, it is naturally identified with the
boundary renormalization group equation of Dirichlet sigma models away from
conformality, to lowest order in perturbation theory. D-branes appear as fixed
points of this flow having conformally invariant boundary conditions. Simple
running solutions include the paper-clip and the hair-pin (or grim-reaper)
models on the plane, as well as scaling solutions associated to rational (p, q)
closed curves and the decay of two intersecting lines. Stability analysis is
performed in several cases while searching for transitions among different
brane configurations. The combination of Ricci with the mean curvature flow is
examined in detail together with several explicit examples of deforming curves
on curved backgrounds. Some general aspects of the mean curvature flow in
higher dimensional ambient spaces are also discussed and obtain consistent
truncations to lower dimensional systems. Selected physical applications are
mentioned in the text, including tachyon condensation in open string theory and
the resistive diffusion of force-free fields in magneto-hydrodynamics.Comment: 77 pages, 21 figure
Cosmological Effects of Radion Oscillations
We show that the redshift of pressureless matter density due to the expansion
of the universe generically induces small oscillations in the stabilized radius
of extra dimensions (the radion field). The frequency of these oscillations is
proportional to the mass of the radion and can have interesting cosmological
consequences. For very low radion masses () these low frequency oscillations lead to oscillations in
the expansion rate of the universe. The occurrence of acceleration periods
could naturally lead to a resolution of the coincidence problem, without need
of dark energy. Even though this scenario for low radion mass is consistent
with several observational tests it has difficulty to meet fifth force
constraints. If viewed as an effective Brans-Dicke theory it predicts
( is the number of extra dimensions), while
experiments on scales larger than imply . By deriving the
generalized Newtonian potential corresponding to a massive toroidally compact
radion we demonstrate that Newtonian gravity is modified only on scales smaller
than . Thus, these constraints do not apply for
(high frequency oscillations) corresponding to scales less than the current
experiments (). Even though these high frequency oscillations can not
resolve the coincidence problem they provide a natural mechanism for dark
matter generation. This type of dark matter has many similarities with the
axion.Comment: Accepted in Phys. Rev. D. Clarifying comments added in the text and
some additional references include
BrainFrame: A node-level heterogeneous accelerator platform for neuron simulations
Objective. The advent of high-performance computing (HPC) in recent years has led to its increasing use in brain studies through computational models. The scale and complexity of such models are constantly increasing, leading to challenging computational requirements. Even though modern HPC platforms can often deal with such challenges, the vast diversity of the modeling field does not permit for a homogeneous acceleration platform to effectively address the complete array of modeling requirements. Approach. In this paper we propose and build BrainFrame, a heterogeneous acceleration platform that incorporates three distinct acceleration technologies, an Intel Xeon-Phi CPU
Investigating Off-shell Stability of Anti-de Sitter Space in String Theory
We propose an investigation of stability of vacua in string theory by
studying their stability with respect to a (suitable) world-sheet
renormalization group (RG) flow. We prove geometric stability of (Euclidean)
anti-de Sitter (AdS) space (i.e., ) with respect to the simplest
RG flow in closed string theory, the Ricci flow. AdS space is not a fixed point
of Ricci flow. We therefore choose an appropriate flow for which it is a fixed
point, prove a linear stability result for AdS space with respect to this flow,
and then show this implies its geometric stability with respect to Ricci flow.
The techniques used can be generalized to RG flows involving other fields. We
also discuss tools from the mathematics of geometric flows that can be used to
study stability of string vacua.Comment: 29 pages, references added in this version to appear in Classical and
Quantum Gravit
Critical behavior of collapsing surfaces
We consider the mean curvature evolution of rotationally symmetric surfaces.
Using numerical methods, we detect critical behavior at the threshold of
singularity formation resembling the one of gravitational collapse. In
particular, the mean curvature simulation of a one-parameter family of initial
data reveals the existence of a critical initial surface that develops a
degenerate neckpinch. The limiting flow of the Type II singularity is
accurately modeled by the rotationally symmetric translating soliton.Comment: 23 pages, 10 figure
Connection between non-Abelian tensor gauge fields and open strings
We compare the structure of the tree level scattering amplitudes in
non-Abelian tensor gauge field theory and in open string theory with Chan-Paton
charges. We limit ourselves considering only lower rank tensor fields in both
theories. We identify the symmetric and antisymmetric components of the second
rank tensor gauge field with the string excitations on the third and forth
levels. In the process of this identification we have been selecting only those
parts of the tree level scattering amplitudes in the open string theory which
have dimensionless coupling constants in four dimensions. It seems that this
subclass of tree level scattering amplitudes may provide important information
about the structure of the open string theory and most probably it is
equivalent to the non-Abelian tensor gauge field theory.Comment: 30 pages, 5 figures, published versio
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